NASA Study Finds Near-Earth Asteroid Is Actually Comet

NASA Study Identifies Near-Earth Asteroid as Comet

A long-studied near-Earth object previously classified as an asteroid has been identified as a comet, according to new research led by scientists at NASA’s Jet Propulsion Laboratory. The object, provisionally known as 1998 SH2, exhibited unexpected orbital behavior that led researchers to conclude it is not a typical asteroid, but rather a body venting gas into space. The findings, published in the journal *Nature Astronomy*, represent the first instance where an object’s cometary nature was confirmed through the observation of its anomalous motion.

Unexpected Orbital Deviations

The object 1998 SH2 had been tracked for 27 years, with its orbit well-documented between 1998 and 2016. However, during a close approach to Earth on August 28, 2025, the object did not appear at its predicted location. Radar observations and data from the NASA Deep Space Network (DSN) revealed a discrepancy of 19 standard deviations from the calculated path, effectively ruling out measurement error. Davide Farnocchia, a navigation engineer with NASA’s Center for Near-Earth Object Studies at JPL and lead author of the study, explained that the object was experiencing “nongravitational perturbations.” Researchers determined that these deviations were caused by the object generating a small amount of thrust by venting gas as the Sun heated ice mixed with rocky material. This process acts like a tiny thruster, pushing the object off its predicted trajectory.

Visual Confirmation of Cometary Activity

While traditional comets are easily recognized by their bright tails and comas, “dark comets” often lack these visible features. To test the hypothesis that 1998 SH2 was an active, albeit faint, comet, researchers coordinated observations with several powerful observatories, including the Canada-France-Hawaii Telescope in Hawaii, the European Southern Observatory’s Danish Telescope in Chile, and the 8.2-meter Very Large Telescope on Cerro Paranal. The resulting deep-stacked images revealed a faint coma and a narrow, weak tail. The dust emission observed between late August and late September 2025 indicated that the activity was driven by continuous sublimation rather than a one-time impact.

Implications for Planetary Defense and Dark Comets

The identification of 1998 SH2 provides significant insight into the class of objects known as “dark comets.” These bodies resemble asteroids but exhibit orbital irregularities characteristic of comets. Researchers suggest that many larger dark comets with orbits similar to 1998 SH2 may be regular comets that simply require more powerful imaging to reveal their faint activity. This discovery has practical implications for planetary defense. If objects classified as potentially hazardous asteroids are actually comets, their trajectories may be subject to unpredictable changes, complicating long-term collision-risk assessments. While 1998 SH2 poses no threat to Earth in the foreseeable future, scientists note that an increase in the number of unidentified comets among hazardous objects necessitates a re-evaluation of current risk models.

Broader Scientific Connections

The research may also offer a natural explanation for the behavior of ‘Oumuamua, the first interstellar object observed passing through the inner solar system in 2017. ‘Oumuamua exhibited unexplained acceleration similar to that seen in dark comets, leading to various theories about its nature. Scientists suggest that the outgassing processes confirmed in 1998 SH2 provide a viable explanation for ‘Oumuamua’s motion without requiring non-natural causes.

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